**2. Materials and Methods**

Samples of synthetic polycrystalline diamond and single crystal Ib diamond were used. A 450 μm-thick polycrystalline diamond plate was prepared by chemical vapor deposition on a silicon substrate 63 mm in diameter [13,14]. A (111) face diamond crystal was obtained by high-pressure, high-temperature growth in Fe–Ni–C liquid from the seed [15,16]. High-fluence irradiation with Ar<sup>+</sup> and C<sup>+</sup> ions was carried out along the normal to the sample surface on a mass monochromator of the Skobeltsyn Institute of Nuclear Physics, Moscow State University [17]. The ion energy was 30 keV. The ion current density reached 0.4 mA/cm<sup>2</sup> at a beam cross section of 0.3 cm2. The irradiation fluences ϕ*t* (ϕ = the ion flux density, and *t* = the irradiation time) were no less than 1018 ions/cm2 for all the cases of diamond irradiation. The flat resistive furnace in the target holder allows heating the target up to 720 ◦C. The target temperature was measured with a chromel alumel thermocouple fixed on the irradiated side of the sample outside of the irradiation area. Samples irradiated at *T* = 30 ◦C were isochronally annealed in a vacuum with a one-hour thermal treatment as the maximum cycle temperature *T* was increased sequentially from 100 to 720 ◦C.

The modified target was examined by SEM with a Lyra 3 (TESCAN, Brno, Czech Republic), AFM with a Dimension V (Veeco, Plainview, NY, USA) and a T64000 Raman spectrometer (Horiba Jobin Yvon, Edison, NJ, USA). Laser radiation with a wavelength of 488 nm for a single diamond crystal and a wavelength of 514 nm for a polycrystalline diamond was used to excite Raman scattering. Electrical measurements of the sheet resistance *R*<sup>s</sup> were used in a four-point probe method at room temperature.
